Is the spotted (sbar sliding on rails) bad for squats

[jamze7417]

Hey guys when i do squats i usually use the rack where the bar slides up and down. You still put plates on it and sutff but its on rails. Im not sure what its called but anyways. I sometimes do my squats on there becuase i have a bad knee that somtimes gives out with out notice and i dontalways have a spotter. I know that im not building the muscle that i could be if i were doing it just freely but is this still effective. ???
thanks

[NiteHawk]

You are talking about the smith machine. Squats on a smith are better than no squats. But if you can stick with regular free bar squats in a power rack.

[bbskupak]

if you do them in a rack and you leg gives out it will be the same as on the smith as far as where the bar falls to...just set the rack slightly below your range of motion and you should be good